ORIGIN  OF  GRAPHITE. 
457 
stone — a  fact  particularly  interesting  to  geologists.  Is  lime- 
stone a  product  of  eruption,  or  is  it  a  sediment  transformed  by 
the  action  of  heat?  The  presence  of  graphite  is  explicable  by 
neither  hypothesis.  For  at  a  certain  temperature,  which  need 
not  be  very  high,  carbon  decomposes  carbonate  of  lime.  This 
salt  may  no  doubt,  under  strong  pressure,  be  heated  to  the 
melting  point  without  losing  its  carbonic  acid ;  this  is  a  labora- 
tory experiment  often  cited  by  the  Plutonists.  But  it  is  quite 
a  different  thing  with  a  mixture  of  carbon  and  carbonate  of 
lime  at  a  high  temperature.  If  we  reject  the  Neptunian  origin 
of  granulated  limestone,  we  must  then,  as  with  crystalline  rocks, 
suppose  that  graphite  has  been  introduced  by  the  wet  way  at  a 
more  recent  period.  The  same  remark  applies  to  magnetic 
pyrites  (sulphide  of  iron),  often  very  rich  in  plumbago  kerns. 
Does  graphite,  like  all  carbon,  belong  to  the  organic  king- 
dom ?  It  is  certain  that  anthracite,  lignite,  coal,  are  the  result 
of  the  slow  decomposition  of  an  enormous  quantity  of  vegeta- 
bles ;  the  impressions  found  on  them  often  indicate  the  kind  of 
vegetables,  most  of  them  extinct,  which  have  contributed  to 
these  carbonaceous  formations.  Graphite,  if  not  formed  in 
precisely  the  same  way  as  coal  and  anthracite,  nevertheless 
bears  signs  of  an  organic  origin.  The  formation  of  nuclei  and 
veins  of  graphite  in  crystalline  rocks  is  sufficiently  explained 
by  the  decomposition  of  carbonized  hydrogen  gas  at  a  high 
temperature ;  this  gas,  disengaged  from  organic  matters,  and 
penetrating  the  fissures  of  the  burning  rock,  would  undergo 
decomposition  into  hydrogen  and  carbon. 
It  is  this  deposited  carbon  which  forms  graphite.  If  in  our 
laboratories  we  do  not  obtain  exactly  the  same  product,  it  must 
be  remembered  that  Nature  has  means  at  her  command  which 
escape  our  researches.  We  find  it  impossible  to  make  coal  from 
wood.  The  wood  may  be  carbonized  by  the  dry  or  by  the*wet 
way.  In  the  first  place  the  carbonization  is  very  rapid  ;  in  the 
latter  it  is  extremely  slow,  as  is  shown  by  the  blackened  points 
of  piling  sunk  in  water. 
Finally,  graphite  has  been  found  in  meteorites  or  areolites. 
Attempts  have  been  made  to  explain  its  presence  here  by  the 
continuance  of  these  stones  in  soil  more  or  less  rich  in  carbon- 
ized principles.    But  with  regard  to  newly-fallen  stones,  this 
